1. Field of the Invention
The present invention generally relates to a mechanical device for the enhancement of a linear force, such as a device used to actuate the punch of a punch and die set. More specifically, this invention relates to a mechanical force enhancer having a link which is sequentially cammed about two fulcrums by which a force delivery member is sequentially operated between a relatively low force stroke and a slower, relatively high force stroke.
2. Description of the Prior Art
The prior art discloses a wide variety of mechanical devices which operate to mechanically amplify a force which is delivered by hand or by a mechanical device such as a fluid cylinder. Generally, such a mechanical force enhancer receives as an input a relatively small linear or rotary force and amplifies or multiplies it to produce a larger linear force. For manufacturing applications, such as a mechanical force enhancer employed to operate a punch and die set, the input force is most often generated by a fluid driven cylinder or an electric or fluid-driven motor to permit some degree of automation.
An taught in U.S. Pat. Nos. 3,453,914 and 3,680,400 to Lemper et al., an input force can be multiplied to produce a larger output force by employing an eccentric which is rotated against a ram member carrying a tool used to perform work on a workpiece. The force enhancers taught by Lemper et al. employ an independently-powered screw mechanism which cooperates with the eccentric to incrementally advance the ram member such that the output of each device is characterized by an incremental movement toward the workpiece coupled with a variable output force at the ram member. A disadvantage with the devices taught by Lemper et al. is that they are rather complicated in their construction and rely upon two separate inputs to produce the force amplification sought. In contrast, U.S. Pat. No. 2,390,371 to Ivy teaches a simpler force amplification device which employs an eccentric that operates a pair of levers to deliver a large linear output force for a punching process. However, the mechanical advantage of the eccentric taught by Ivy is rather minor in terms of force amplification.
Mechanical force enhancers are often used to operate a tool which performs work on a workpiece, such as a punch and die set noted above. With such applications, it is typically preferable that the tool be slowed near the end of its stroke to prevent unnecessary impacting of the workpiece. An example of such a device is taught in U.S. Pat. No. 4,932,128 to Dacey, Jr. Dacey, Jr. teaches a pneumatic cylinder which is mounted to a housing having a pair of spaced-apart side plates. The cylinder's piston rod is attached to a first end of a link which is guided by one of a pair of complementary grooves in the side plates. The second end of the link is guided by the second of the pair of complementary grooves, and a ram is attached to the link intermediate the first and second ends of the link. After the link has been translated a prescribed distance, the second end of the link is stopped, forcing the link to pivot about the second end. As a result, after the second end of the link is stopped, the speed of the ram is decreased and the force input of the cylinder is amplified to the ram by the effect of the link rotating about its second end. However, a drawback to the force enhancer taught by Dacey, Jr. is that the device is rather complicated, the ultimate force output is limited by the relatively small size of the link, and the particular structure necessitated by the pivot feature of the link is rather complicated, requiring an added level of precision.
As taught in U.S. Pat. No. 3,482,830 to Sendoykas, camming mechanisms are also known in the prior art as being useful to alter the output speed of a device whose output is in the form of a force. Sendoykas teaches a cylinder whose linear input is operated on through a camming device and two separate pivots to alter the speed of a clamp. The pivots serve as sequential fulcrums about which the body of the clamp pivots as the cylinder extends and retracts. However, the output force is not intentionally amplified by the device in that the moment created by the cylinder about each fulcrum is roughly the same.
From the above discussion, it can be readily appreciated that the prior art does not disclose a mechanical force enhancer which is capable of producing an amplified output to a work-performing ram while also being uncomplicated in its construction and operation. Nor does the prior art disclose such a device which is particularly suitable for use as a punch and die press, wherein the output speed of the ram is reduced near the end of the stroke to prevent excessive impact loads on a workpiece.
Accordingly, what is needed is a cost-efficient mechanical force enhancing device suitable for use as a punch and die press, the mechanical force enhancement device being capable of amplifying an input force and delivering the amplified force to a ram member which includes a work-performing tool, wherein the force amplification is derived from operating the device off two stationary fulcrums which are rugged and uncomplicated in their design and which also serve to reduce the output speed as the tool nears the workpiece.